1. Field of the Invention
The present invention relates to a communication device and a communication system and, particularly, to a communication device and a communication system used in close proximity.
2. Description of the Related Art
When moving data between small-size information devices, a method of moving data through data communication by interconnection between the information devices using a general-purpose cable such as a USB cable or through a medium such as a memory card is generally used.
In addition, information devices incorporating various cable-less communication functions are provided. As a method of performing cable-less data communication between small-size information devices, radio frequency communication that transmits and receives radio signals using antennas, including wireless LAN such as IEEE802.11 and Bluetooth (registered trademark) communication, is developed. In the radio frequency communication, a wireless interface can be used when exchanging data such as images and music with a personal computer, and there is no need to insert and withdraw a connector to connect a cable for each data communication, thus offering enhanced user-friendliness.
Further, a close proximity wireless communication system that uses a high frequency coupler rather than an antenna and achieves wireless communication in a short distance of several centimeters utilizing electric field coupling by an electrostatic field or an induction field has been proposed recently (cf. e.g. Japanese Patent No. 4345849). In the close proximity wireless communication system, a communication distance is as short as several centimeters to prevent crosstalk with wireless LAN, Bluetooth (registered trademark) communication or the like. Therefore, the close proximity wireless communication system enables broadband communication without interference with another communication system. Further, the close proximity wireless communication system enables high-speed data transfer, thus achieving transfer of high-volume data in a short time, such as transfer of digital camera images or transfer of digital video camera high-definition pictures.